An Overview on Geophysical Investigations of Earthen Dam Foundations in California for the U.S. Army Corps of Engineers

The Sacramento District, U.S. Army Corps of Engineers (USACE) teamed with the Crustal Geophysics and Geochemistry Science Center of the U.S. Geological Survey in 2005 in order to conduct geophysical Investigations along the downstream toe of Success Dam. An underlying goal of these surveys was to demonstrate the effective use of geophysics for answering geotechnical questions for a skeptical audience of geotechnical engineers. the successful completion of that survey led to follow-on work at Isabella, Hidden and Martis Creek Dams, all located in California and operated by the Sacramento District. A range of techniques including P- and S-wave refraction and reflection seismic, DC resistivity, time-domain electromagnetic, electromagnetic induction, self potential, ground and airborne magnetics, magnetotelluric, and ground-penetrating radar have been used to characterize the subsurface in the vicinity of these dams. At Isabella Dam, water borne surveys including magnetics and seismic reflection were also used. At Isabella and Martis Creek Dams, airborne and ground based LiDAR have been used to locate and map fault related structures. This talk will review the work that we have done, provide a summary and demonstration of significant findings, and review some of the lessons learned over the past 5-years of these Investigations.